The retinal pigment epithelium (RPE) plays a crucial role in supporting vision through a variety of activities that maintain retinal health. A loss of RPE cells occurs early in age related macular degeneration (AMD) with a concomitant loss of vision. AMD is the leading cause of blindness in the elderly and its incidence is expected to increase as the US population ages, with great associated personal and economic costs. AMD can be divided into two categories: `dry' AMD constitutes ~90% of cases and `wet' AMD the remaining ~10%. Currently no effective treatment is available for dry AMD, but stem cell therapy holds great promise to replace the RPE cells lost in dry AMD pathogenesis. To this end, we have identified an adult RPE stem cell (RPESC) as a potential source for RPE cell replacement. Our previous work utilizing an animal model of AMD demonstrated the ability of transplanted RPESC-derived RPE (RPESC-RPE) to rescue vision. We found that a progenitor stage of RPESC-RPE maturation is more effective than fully differentiated, mature progeny at vision rescue. In this proposal, we aim to first survey the RPE subpopulations present in the native human RPE layer, including the RPESC, using single cell transcriptomics (Aim 1) and a cell surface screen (Aim2). In Aim 3, we assess the cellular and molecular pathways that underlie vision benefit by transplanted RPE vision. In preliminary experiments using an in vitro integration assay that efficiently evaluates each RPE subpopulation, we found the RPE progenitor stage integrates more effectively than differentiated RPE progeny. We plan to confirm these in vitro results and describe integration of individual subpopulations after transplantation in the animal model. Furthermore, the transcripts that identify the effective RPE subpopulation describe the set of genes that are associated with vision rescue. We use a bioinformatics approach to identify these genes and then propose knock-down and overexpression experiments to assess their function in vitro and in vivo. Completion of these studies will significantly increase our understanding of the RPE at cellular, molecular and functional levels.